1. Field of the Invention
The present invention relates to a method of testing and a testing apparatus for a magnetoresistive effect head, and in more detail to a method and testing apparatus that apply an external magnetic field to (hereinafter, simply “magnetize”) a magnetoresistive effect head as external stress and then measure the output voltage of the magnetoresistive effect head and repeat such magnetizing and measuring a plurality of times to test the quality of the shield film of the magnetoresistive effect head.
2. Related Art
In recent years, magnetoresistive effect heads that use a magnetoresistive effect, as represented by so-called “MR heads”, have been commercialized as thin-film magnetic heads for use with magnetic media such as magnetic disks.
However, although MR heads use the magnetoresistive effect of a magnetic thin film and can obtain a large reproduction output without being dependent on the relative velocity of the head to the magnetic medium, there is a problem that defective MR heads are produced where the magnetic domain of a shield film, i.e., a magnetic layer disposed on both sides of the MR element, can be changed by an external magnetic field, resulting in variation in the output of the MR head.
Since MR heads where the output may vary cannot be expected to carry out reproduction operations properly, such heads need to be rejected during the tests carried out as part of the manufacturing process.
However, since it has not been possible to quantitatively ascertain which MR heads have unstable characteristics where the magnetic domain of the shield film (hereinafter, simply “shield magnetic domain”) changes, the method of testing MR heads has been problematic.
The following method has been used as a conventional method of testing a MR head. An operation that applies a magnetic field in a direction that is parallel to the shield film of the MR head and makes an angle of 0° to a float surface of a magnetoresistive effect head (hereinafter this is referred to as “normal magnetization”) and measures the output voltage of the MR head is repeatedly carried out and the difference between the highest and lowest output voltages is calculated as the variation and used to evaluate how the output varies.
However, the above method has had a problem in that it is not possible to completely detect MR heads where the shield magnetic domain is susceptible to changing.
The inventors of the present invention found that by implementing a method of testing the quality of the shield film of the magnetoresistive effect head composed of a procedure of repeatedly carrying out an operation where an external magnetic field that is parallel to the shield film of the magnetoresistive effect head but makes an extremely small angle to the float surface is applied (hereinafter such operation is referred to as “minute angle magnetization”) and the output voltage of the magnetoresistive effect head is then measured, it becomes possible to detect magnetoresistive effect heads where the shield magnetic domain is susceptible to changing that could not be detected by the conventional method of testing via normal magnetization (see FIGS. 4A to 4D).
The present invention uses this principle and by setting the minute angle and the intensity of the applied magnetic field in appropriate ranges provides a favorable testing apparatus and method of testing a magnetoresistive effect head.
One example of a method of testing a magnetoresistive effect head is disclosed by Japanese Laid-Open Patent Publication No. H10-124828 and is shown in FIG. 6.
This reference proposes a method where a magnetic field is applied as stress in an inclined direction to MR stripes and the characteristics of the MR heads are measured.
Due to the MR heads being formed on a wafer with a large diameter (for example, 5 to 6 inches), the direction of magnetization of the MR stripes is susceptible to becoming non-uniform between central peripheries and outer peripheries of the heads and the magnetic domain control film described above is also susceptible to becoming non-uniform. For this reason, the problem to be solved by Japanese Laid-Open Patent Publication No. H10-124828 is to test such non-uniformities.
In this way, such object differs to the object of the present invention which is “to detect magnetoresistive effect heads where the shield magnetic domain is susceptible to changing that could not be detected by testing methods that use normal magnetization”.
Patent Document 1
Japanese Laid-Open Patent Publication No. H10-124828